looking for guidance analysing dots

summer

I'm not quite sure how to crack this one.

imagine yourself a 2D starcluster with its heavy stardensity in the middle. the longer you get away from the center the cluster gets less dense.

i have all the coordinates and what i need to find is the stars that are not considered within the cluster.

I know this is a little fussy, since I would have to set some kind of spacing variable that defines what's considered too far away between two stars.

In this particular case I have a single star which has a distance from the center that is more than 3 times the size of the cluster.

How would I identify that star?

I know it's weird using php for this stuff but I guess I'd be using some smart array features which php is full of. (and I don't really know any other language =)

Regards,
Summer

barand

Something like

$stars = array(
         'star1' =>   array('x' => 50, 'y' => 50, 'min' => 999),
         'star2' =>   array('x' => 60, 'y' => 30, 'min' => 999),
         'star3' =>   array('x' => 90, 'y' => 110, 'min' => 999),
         'star4' =>   array('x' => 40, 'y' => 40, 'min' => 999),

);

function dist($x1, $y1, $x2, $y2) {
         return floor(sqrt((($x2 - $x1) * ($x2 - $x1)) + (($y2 - $y1) * ($y2 - $y1))));
}

function minsort($a,$b) {
         if ($a['min'] == $b['min']) return 0;
         return ($a['min'] > $b['min']) ? -1 : 1;
}

# find distances to nearest neighbour
$copy = $stars;
foreach ($stars as $k1 => $data1) {
         foreach ($copy as $k2 => $data2) {
                  if ($k1 != $k2) {
                      $d = dist($data1['x'], $data1['y'],$data2['x'], $data2['y']);
                      $stars[$k1]['min']  = min($stars[$k1]['min'], $d);
                  }
         }
}

#use custom sort function minsort() to put remotest first
uasort ($stars, 'minsort');
echo '<pre>';
print_r ($stars);
echo '</pre>';

hth

summer

you, sir, are now my friend =)

with a bit of tweaking I got it to fit in nicely in my project. I can know now see which stars are alone =)

Maybe I could expand the function sometime so I could track small cluster of fx. 3 stars that are not in the main cluster. But in my case this almost never happens.

thaaaanks!

Summer